The present invention relates to an ink-jet printing apparatus and a discharge recovery method for an ink-jet printhead.
Printing apparatus having functions of a printer, a copier, a facsimile and the like, or printing apparatus used as output devices of integrated electronic device or work station including a computer, a word processor and the like, print an image (including characters and the like) on a print material (print medium) such as print paper and plastic sheet based on image information (including character information and the like).
The printing apparatus classify into ink-jet type printers, wire-dot type printers, thermal printers, laser-beam type printers and the like, in accordance with printing method. Among these printers, the ink-jet type printers (ink-jet printer) perform printing by discharging ink from printing means (printhead) onto a print medium. The printing means can be compact in size. Further, these printers can print a high definition image, at a high speed, on a normal print sheet without any special processing. Further, the printers have many advantages such as a low running cost, non-impact low-noise printing, and easy color image printing using ink of multiple colors. Above all, a line-type printer using a full-multi-type printing means with a number of discharge orifices arrayed in a paper width direction can attain higher printing speed.
Among the ink-jet methods used in the above ink-jet type printers, some methods generate heat in discharging ink droplets. The heat generation includes positive heat generation for ink discharge, i.e., ink discharge by utilizing thermal energy, and heat generation accompanying ink discharge. A typical example of printer according to a method for discharging ink by utilizing thermal energy is an ink-jet printer which causes film boiling in ink by thermal energy generated by electrothermal transducers as discharge energy generators, and discharges ink based on radical formation of bubble by the film boiling. Further, an example of an ink discharge method accompanied with heat generation is a well-known method employing piezoelectric devices as discharge energy generators. In this method, when the piezoelectric device vibrates for ink discharge, it generates heat, although the amount of thermal energy is small.
In these ink-jet printers, if ink discharge is continuously performed in case of printing at a comparatively high printing duty such as printing of a graphic image or image including a solid-print portion, a driving interval to drive the discharge energy generators becomes short. In this case, next ink discharge is performed before excessive heat generated upon ink discharge is sufficiently radiated. As heat is accumulated in ink within ink channels having the discharge energy generators, the temperature of the ink rises. At this time, minute bubbles generated from air dissolved in the ink within the ink channels grow, and further, the bubbles grow by coalescing with each other. The grown bubbles stay in the ink channels to influence ink discharge, further, change discharge directions and discharge amounts. Thus, ink discharge becomes unstable.
Conventionally, to prevent the inconvenience due to the above-described residual bubbles, the residual bubbles have been removed from the ink channels by forcibly sucking ink within the ink channels via discharge orifices by using a predetermined suction mechanism or by applying pressure to the ink channels by using a predetermined pressurization mechanism. However, as the amount of ink discharged by the suction-or pressurization operation is comparatively large, the amount of ink unnecessarily consumed for such purpose other than printing is large. As a result, the running cost of the printer increases. Further, to perform suction or pressurization, a comparatively large number of operations including movement of a printhead to a capping position, capping, suction and pressurization are required. If the processing is performed during printing, the printing speed becomes lower in the entire printer. To address these problems, a technique to perform discharge recovery by discharging the above-described bubbles by continuously performing ink discharge plural times from the ink channels, except a bubble-discharge target channel but including at least its adjacent ink channels (Japanese Patent Laid-Open No. 4-219253) is disclosed.
However, to output an image with inconspicuous jaggies in black characters and the like or to output a color image as a more pictorial high-quality image, if the print pixel density is raised by changing the conventional 40 pl to 60 pl discharge amount to that of smaller droplets, the following problem occur.
First, materials dissolved in ink is precipitated by heat accompanying ink discharge, and the precipitate accumulated around the discharge orifices, the discharge energy generators or within the ink channels also influences ink discharge. For example, if polyurethane sponge is used in an ink tank, polyol, yielded by hydrolytic degradation by heat at a polyurethane sponge manufacturing process, exists as dissolved material in the ink. The polyol dissolved in the ink is precipitated by heat accompanying ink discharge. In the conventional discharge amount, the amount of discharged ink is overwhelmingly larger than the amount of precipitate, therefore the precipitate does not influence ink discharge. However, in the discharge amount of smaller droplets, the precipitate greatly disturbs the precision of ink application position.
Secondly, the influence of the above-described residual bubbles on ink discharge changes in accordance with a printing history of past printing about the number of printing pulses, the printing time, the printing area and the like, and the time elapsed from the completion of printing. If discharge recovery operation is performed regardless of history of past printing and time elapsed from the completion of printing as in the case of the conventional art, the discharge recovery cannot be sufficiently performed, or the amount of unnecessarily consumed ink increases. Also, the influence of the above-described precipitate on ink discharge greatly differs in accordance with history of past printing and time elapsed from the completion of printing.
Further, the amount of precipitate differs in. accordance with ink type, and the influence of the precipitate on ink discharge differs in accordance with the amount of precipitate.
The present invention has been made to solve the above-described problems, and has its object to provide an ink-jet printing apparatus and a discharge recovery method for an ink-jet printhead which prevent reduction of printing speed and increase in ink consumption amount by unnecessary discharge recovery processing, and which maintain excellent image quality.
According to the present invention, the foregoing object is attained by providing an ink-jet printing apparatus having a printhead with a plurality of discharge orifices, including heat sources, for discharging ink droplets, comprising: detection means for detecting a driving state of the printhead per unit period; determination means for determining whether or not the driving state detected by the detection means has become a predetermined state; control means for performing discharge recovery processing on the printhead if it is determined by the determination means that the printhead has entered the predetermined state.
Further, according to the present invention, the foregoing object is attained by providing a discharge recovery method for an ink-jet printing apparatus, having a plurality of discharge orifices including discharge energy generators corresponding to the discharge orifices, for performing printing by discharging different types of ink from a plurality of printheads onto a print medium, wherein if the conditions of the history of past printing meet predetermined conditions, preparatory discharge is performed in a predetermined pattern, for discharge recovery.
Preferably, the conditions of the printing history of past printing, the predetermined conditions and the preparatory discharge in the predetermined pattern, differ by each ink type.
Preferably, the conditions of the printing history of past printing include the number (n) of printing pulses and the printing time (t) in the past printing; and the predetermined conditions include a predetermined value (a)xe2x89xa6{the number (n) of printing pulses/printing time (t)}. More preferably, the predetermined conditions include the predetermined value (a)xe2x89xa6{the number (n) of printing pulses/printing time (t)} and a predetermined number (b)xe2x89xa6the number (n) of printing pulses.
Preferably, the predetermined conditions include the number (n) of printing pulse and the printing time (t) in the past printing means the number of scan movements of the printhead, or the number (n) of printing pulses and the printing time (t) in printing for a predetermined number of pages.
Further, the preparatory discharge in the predetermined pattern may be performed if the predetermined conditions are satisfied while the printing time (t) or the number (n) of printing pulses in the past printing has a fixed value.
Further, the conditions of the printing history in past printing may include the number (n) of printing pulses and the print area (w) in the past printing. The predetermined conditions include a predetermined value (d)xe2x89xa6{the number (n) of printing pulses/print area (w)}, or preferably, the predetermined value (d)xe2x89xa6{the number (n) of printing pulses/print area (w)} and a predetermined value (e)xe2x89xa6the number (n) of printing pulses.
Preferably, the preparatory discharge in the predetermined pattern is dividing the array of plurality of discharge orifices (L) into s (s is a divisor of L) groups, and among discharge orifices having numbers obtained by (sxc3x97xxe2x88x92y) (x is an integer from 1 to L/s), continuously driving discharge energy generators, from an orifice with a number obtained when y=0 holds to an s-1 th orifice, plural times alternately, and not driving the orifices for a predetermined period of time, at fixed intervals, thus performing discharging from all the discharge orifices.
Preferably, the discharge recovery may be made by performing the preparatory discharge in the predetermined pattern which differs in accordance with the time elapsed from detection of fulfillment of the conditions. More preferably, by performing the preparatory discharge in the predetermined pattern where the number of driving pulses increases as the elapsed time increases.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.